This invention relates to a valve stem seal assembly for valves of internal combustion engines wherein high pressures prevail in the intake and/or outlet ports. The seal assembly includes a rigid housing in which an elastomer sealing body is arranged that has at least two sealing lips engaging the valve stem and being effective in opposite directions. One of the sealing lips which is closer to the combustion chamber served by the valve functions as a gas-sealing lip, whereas the other sealing lip which is more remote from the combustion chamber functions as an oil-sealing lip. The elastomer sealing body further has an adhering portion insertable on a valve guide sleeve and an elastic diaphragm which permits radial displacements and which is connected with the oil-sealing lip.
German Utility Patent No. 1,966,994 discloses a valve stem seal assembly having two sealing lips engaging the valve stem. The sealing lips are situated immediately axially adjacent and the gas-sealing lip is formed from the oil-sealing lip. Both sealing lips are radially displaceably guided by a highly elastic intermediate component constituted by a diaphragm so that the two sealing lips are interconnected and thus are vibration-dependent from one another.
It has been found that in internal combustion engines where a high pressure exists in the intake and/or outlet ports, for example, in turbo engines, the pressure prevailing in the intake and outlet port may reach such a high value that the sealinq lips lift off the valve stem. Upon a pressure increase on the combustion chamber side the gas pressure may, in the known seal constructions, directly affect the intermediate member (that is, the diaphragm) as a result of which the latter is pushed outwardly or, in case of a vacuum, drawn inwardly. Upon such an occurrence the gas-sealing lip then serves as a fulcrum for a radial displacement of the oil-sealing lip so that the pressing of the oil-sealing lip against the shaft stem is adversely affected, whereby significant fluctuations in the oil dosages may occur.